There is one practical disadvantage in converting the tannins to their salts – they
become anionic surfactants. Detergents and soap are surfactants and these cause materials
that do not dissolve in water (like oil, grease and dichloromethane) to form an emulsion with
water. As we want to be able to separate the aqueous phase from the dichloromethane phase,
it is better not to let the emulsion to occur during the extraction. Consequently, as you extract
the caffeine from water into dichloromethane, do not shake the separatory funnel too
vigorously.